How does useSWR knows when to rerender?

[ngoctuan001]

hi Im new to this library and currently using polling via useSWR, i notice an interesting point and want to ask.

in this link https://swr.vercel.app/docs/advanced/performance#dependency-collection

swr mentioned SWR only updates the states that are used by the component,

how is this possible, how does SWR know which states are used by component ?